This project seeks to characterize and quantify psychophysiological differences that occur across the alter personality states of individuals with multiple personality disorder (MPD). Alter personalities of MPD patients are studied using a range of psychological, physiological and biological measures including: spontaneous EEG, auditory and visual evoked potentials, cerebral blood flow, histamine sensitivity, psychological tests and indices of autonomic nervous system activity. Simulating normal controls subject serve as a comparison group. Recent findings include the demonstration of unusual deficits in implicit memory function in MPD patients.